JP2007309997A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus not producing troubles in the front and back of the large image fixing roller pair largely changing the peripheral speed when shortening the transfer path or bending it for miniaturization, such as image noises, transfer noises, magnification misalignments, color shifts in color images, and abrasions by the guides. <P>SOLUTION: The image fixing unit is made movable upstream or downstream in the transfer direction and moved by detecting the amount of the loop or the transfer speed at the fixing unit. Further, providing fixing unit moving means at both its sides and loop detectors at both ends of the transfer path, the fixing unit moving means are independently controlled when the loop amounts are different in the width direction. The loop produced by the transfer speed variations of the recording sheet in the fixing unit between the secondary transfer (transfer section to the recording sheet) and the fixing unit is kept constant without controlling the speed of the fixing unit. The drive source can be shared by the fixing unit and other units. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a recording material conveying method and driving configuration before and after fixing of an image forming apparatus.

  FIG. 10 is a cross-sectional view showing the configuration of the image forming unit of the image forming apparatus, which will be described in the image formation of a color image.

  For example, photosensitive drums a (yellow), b (magenta), c (cyan), and d (four image forming media arranged in parallel to form toner images of colors of yellow, magenta, cyan, and black, respectively. Black) and an intermediate transfer belt 2 which is a transfer conveying means arranged in a manner of cutting the photosensitive drums a to d vertically.

  A primary charger, a developing device, and a transfer charger (not shown) are arranged around the photosensitive drums a, b, c, and d driven by a motor (not shown), and these units are united as process cartridges 1a to 1d. It has become.

  An exposure device 6 composed of a polygon mirror or the like is disposed below the photosensitive drums a to d.

  First, laser light based on a yellow component color image signal of an original is projected onto the photosensitive drum a through a polygon mirror of the exposure device 6 to form an electrostatic latent image on the photosensitive drum a, and a developing device Then, the yellow toner is supplied and developed, and the electrostatic latent image is visualized as a yellow toner image.

  When this toner image arrives at the primary transfer portion where the photosensitive drum a and the intermediate transfer belt 2 come into contact with the rotation of the photosensitive drum a, the primary transfer bias applied to the transfer charging member 2a causes the toner image on the photosensitive drum a. The yellow toner image is transferred to the intermediate transfer belt 2 (primary transfer).

  When the portion of the intermediate transfer belt 2 carrying the yellow toner image moves to the image forming unit, a magenta toner image is formed on the photosensitive drum b by the same method as described above in the image forming unit, and this magenta toner image Is transferred onto the intermediate transfer belt 2 from the yellow toner image.

  Similarly, as the intermediate transfer belt 2 moves, the cyan toner image and the black toner image are transferred onto the yellow toner image and the magenta toner image, respectively, at each primary transfer portion of the image forming unit.

  On the other hand, the recording material P is stored in the cassette 4.

  The recording material P is fed one by one from the cassette 4 by the pick-up roller 8, is timed by the registration roller 9, reaches the secondary transfer portion, and is applied by the secondary transfer bias applied to the secondary transfer roller pair 3. The four color toner images on the intermediate transfer belt 2 are collectively transferred onto the recording material P (secondary transfer).

  The recording material P on which the four color toner images have been transferred is guided by the transport guide 20 and transported to the fixing device 100 where it is fixed by receiving heat and pressure. After being a full-color print image fixed to P, it is discharged onto the discharge tray 7 by a pair of discharge conveyance rollers 8 provided downstream of the fixing device 100.

  Further, the rotation direction of the paper discharge roller pair 8 is switched using an electromagnetic clutch or the like as necessary, and the flapper 90 is operated to guide the rear end of the recording paper P into the refeed conveyance path 31 and again to the registration rollers. 9 and recording on the back side can be performed.

  In recent years, the fixing device 100 for heat fixing has higher heat transfer efficiency than the heat roller type fixing device from the viewpoint of energy saving promotion, the start-up of the device is quick, and the wait time is shortened (operated on demand). A film heating type fixing device capable of saving power has been proposed and put into practical use (see, for example, Patent Document 1 and Patent Document 2).

  In this fixing device, a material to be heated is closely attached to a heating body fixedly supported by a support member via a heat-resistant and thin film material, and the film material is slid to the heating body to heat the heating body to the film material. And is applied to a heated material via a toner image, and can be used as a fixing device that heat-fixes an unfixed toner image as a permanently fixed image on the surface of a transfer material carrying the image.

  In such a film heating type fixing device, the heating body has a low heat capacity with a high temperature rise, for example, a ceramic substrate having characteristics such as heat resistance, insulation and good thermal conductivity, and a surface of the substrate. A so-called ceramic heater having a resistor (heating element) that generates heat when energized can be used, and a thin film with a low heat capacity can be used as a film material. Therefore, there is no need to supply power to the heating element during standby, and even if the transfer material passes immediately, the heating element is sufficiently heated up to the predetermined temperature until the transfer material reaches the fixing site. Thus, the wait time can be shortened and the power can be saved. Further, it has an advantage that the temperature rise inside the image forming apparatus can be lowered and is effective.

  FIG. 11 is a cross-sectional schematic diagram of a main part of an example of a film heating type fixing device (fixing device).

  Reference numeral 102 denotes a heating body (hereinafter referred to as a heater), and 103 denotes a rigid and heat-resistant heating support member (heating body holder (stay), hereinafter referred to as a heater holder) in which the heater 102 is fixedly supported in a groove on the lower surface side. , 101 is a heat-resistant and thin-walled film material (hereinafter referred to as a fixing film), and 104 is a pressure roller, which is composed of a core metal, an elastic layer such as silicon rubber, and a release layer.

  The heater 102 fixedly supported on the lower surface side of the heater holder 103 and the pressure roller 104 are pressed against each other with a predetermined pressing force against the pressure roller 104 with the fixing film 101 interposed therebetween, and a heating nip portion having a predetermined width ( (Hereinafter referred to as a fixing nip portion) N is formed.

  A ceramic heater is generally used as the heater 102, and is heated and adjusted to a predetermined temperature by energization.

  The fixing film 101 has a very thin thickness of 20 to 70 μm in order to efficiently apply the heat of the heater 102 to the transfer material P at the fixing nip portion N.

  The fixing film 101 has a three-layer structure of a film base layer, a primer layer, and a release layer. The film base layer side is a heater side, and the release layer side is a pressure roller side.

  The film base layer is made of polyimide, polyamideimide, PEEK (polyetheretherketone) or the like having higher insulation than the glass protective layer 102b of the heater 102, and has heat resistance.

  Further, the mechanical strength such as the tear strength of the entire fixing film 101 is maintained by the film base layer.

  The primer layer is formed as a thin layer having a thickness of about 2 to 6 μm.

  The releasable layer is a toner offset prevention layer for the fixing film 101, and is coated with a fluorine resin such as PFA (perfluoroalkoxy), PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene) to a thickness of about 10 μm. It is formed.

  At the fixing nip N, the transfer material P and the toner image are heated by the heater 102 via the fixing film 101, and the toner image is heated and fixed on the surface of the transfer material P.

  The rotational drive is given to the pressure roller.

  The thermal energy and pressure energy that the recording material P receives from such a fixing device includes the fixing temperature, the nip width formed between the fixing rollers, the speed passing through the fixing device (the conveyance speed of the pressure roller 104). ) And so on.

  Further, it is already known that the quality of the image formed on the recording material P changes depending on the heat energy and pressure energy received from the fixing device, and in particular, a large amount of toner adheres to the recording material P. The color image to be formed is more susceptible to not only the image quality, particularly gloss, but also the conveyance speed of the recording material, compared to a black and white image with a small toner adhesion amount.

  Further, the image quality and the conveyance speed of the recording material also change depending on the difference in heat capacity of the recording material P, that is, whether the recording material P is thin paper, thick paper, or OHP film.

  As a drive configuration of this apparatus, there is one configured to obtain power from a common drive source for the intermediate transfer belt and the fixing device having a heavy load torque in order to reduce cost and save space.

Further, the paper discharge roller disposed downstream of the fixing device also obtains power from a common drive source.
JP 2002-091207 A (see FIG. 8) Japanese Patent Laid-Open No. 2003-043843 (see FIG. 1)

  In general, when the toner image on the recording material P is fixed by the fixing roller pair, the recording material P and the unfixed toner are deprived of heat energy, and accordingly, the temperature of the fixing roller pair decreases. To do.

  In particular, when the image forming operation is executed continuously, the energy lost by the fixing process of one recording material is not sufficiently recovered, and the next recording material is fixed while the fixing roller temperature is lowered. Processing may be started.

  As a countermeasure, by increasing the power supplied to the heater (increasing the heater capacity), the supply energy and the consumed energy can be balanced over a relatively long interval. If a material with poor thermal response such as heat resistant rubber is used on the surface of the roller, the temperature of the fixing roller may temporarily decrease.

  For this reason, a change in temperature generated in the fixing roller appears as a change in the outer diameter of the fixing roller, so that the conveying speed of the recording material passing through the fixing roller pair changes.

  Further, in the fixing device using the film heating method used in the conventional example, since the warm time is short, when the recording material is continuously fed from the cold state, the pressure roller to be driven is warmed up in the initial state. In this case, the pressure roller changes greatly during continuous paper feeding because it is not thermally expanded.

  That is, the outer diameter of the driven pressure roller is greatly different between the first and last sheets.

  In particular, a fixing device of a color image forming apparatus uses heat-resistant rubber such as silicon rubber for the surface layer of the roller. However, since heat-resistant rubber has a large coefficient of thermal expansion, the pressure roller due to temperature change of the pressure roller. -The change in the outer diameter of the roller is large, and the conveyance speed of the recording material in the fixing device changes greatly.

For this reason, when the temperature of the pressure roller decreases and the outer diameter of the pressure roller is reduced below the reference dimension, the recording material conveyance speed by the secondary transfer roller pair and the paper discharge conveyance roller pair is higher in the fixing device. Since it is faster than the recording material conveyance speed, a loop L is generated in the recording material P between the secondary transfer roller pair and the fixing device, and the recording material P is pulled between the fixing device and the paper discharge roller pair. (Fig. 12)
At this time, if the unfixed toner on the recording material adheres to the peripheral conveyance guide or the like between the pair of secondary transfer rollers and the fixing device and causes defective images, or if thick paper with high rigidity is flown, If the conveying force of the pair is low, the transfer roller portion slips and the image shrinks.

  Also, since the fixing device and the pair of conveyance rollers are pulled between the fixing device and the paper discharge conveyance roller pair, the conveyance path bent in the vicinity thereof when the toner is melted by heat and not completely fixed. In such a case, rubbing with the conveyance guide or the like occurs between the secondary transfer roller pair and the fixing roller pair.

On the other hand, when the fixing roller temperature rises and the outer diameter of the fixing roller becomes larger than the reference dimension, the recording material conveyance speed by the secondary transfer roller pair and the discharge conveyance roller pair is fixed. Since it is slower than the recording material conveyance speed in the apparatus, the recording material P is pulled between the secondary transfer roller pair and the fixing roller pair, and the recording material P is looped between the fixing roller pair and the discharge conveyance roller pair. L is generated. (Fig. 13)
At this time, the recording material is forcibly pulled out from the transfer position by the fixing roller between the secondary transfer roller pair and the fixing roller pair, and transfer noise (disturbance of the image at the time of transfer) occurs or copying occurs. In the case of a magnification shift or a color image, a color shift occurs.

  In addition, since the toner image fixed on the recording material by the fixing roller pair between the fixing roller pair and the paper discharge conveyance roller pair is immediately after fixing, the toner is melted by heat and is not completely fixed. Swelling occurs between the guides, and the conveyance guides and the like are rubbed.

  The above phenomenon occurs more remarkably when the conveyance path is shortened for downsizing of the apparatus.

  In addition, the recording material is not necessarily sent straight in the conveyance direction due to the parallelism of the secondary transfer unit and the fixing unit, the respective pressure balances, tolerances such as roller diameter, variations, etc., on both sides of the recording material in the width direction. In some cases, the sheet is transported in a state where a speed difference has occurred.

  In such a state, a loop generated between the secondary transfer portion and the fixing device may be different in the width direction, while being rubbed against the guide, and on the other hand, the recording material may be pulled.

  Such a phenomenon occurs more remarkably when recording on a long paper or the like that is extremely long in the transport direction in recent years.

  In the present invention, when the conveyance path is shortened or the conveyance path is bent in order to reduce the size of the apparatus, problems that occur in the conveyance paths before and after the fixing roller pair having a large peripheral speed fluctuation, that is, image noise and transfer. It is an object of the present invention to provide an image forming apparatus that does not cause noise, a copy magnification shift, a color shift in the case of a color image, a conveyance guide rubbing, and the like.

  In addition, even on long recording paper such as long paper, image formation that does not cause image noise, transfer noise, copy magnification deviation, color deviation in the case of color images, conveyance guide rubbing, etc. An object is to provide an apparatus.

  An image carrier that carries a latent image; a developing unit that visualizes the latent image on the latent image carrier as a developer image; a transfer unit that transfers the developer image to a recording material as an unfixed image; An image forming apparatus comprising: a fixing unit that fixes a received image on a recording material by heating; and a paper discharge conveying unit that discharges the recording material to the fixing unit. And a loop detecting unit that detects a slack state of the recording material between the transfer unit and the fixing unit, and the movement of the fixing unit is controlled by the loop detecting unit that detects the slack state. .

  A loop detection unit for detecting the sagging state, the moving unit enabling the fixing unit to move in the conveying direction of the recording material; and a loop detecting unit for detecting a sagging state of the recording material between the transfer unit and the fixing unit. By controlling the movement of the fixing means, the various image defects caused by the loop state of the recording material from the time when the recording material is nipped to the fixing means having a large peripheral speed fluctuation to the time when it passes through the nip of the transfer means are solved. can do.

  By using the same drive source for the fixing device and the transfer unit, a space-saving and low-cost image forming apparatus can be provided.

  The moving means is provided at both ends of the fixing device in the width direction of the recording material, and the loop detecting means is provided at portions corresponding to both ends of the recording material, and the moving means is based on the detecting means corresponding to each side. Therefore, it is possible to prevent a different loop shape in the width direction from occurring when the transport speed is not uniform in the width direction. Various image defects caused by the loop state of the recording material until it passes through the nip of the recording medium can be solved. This is particularly effective when recording on recording paper having a long length in the conveying direction of long paper or the like.

  A moving means that enables the fixing means to move in the conveying direction of the recording material and a detecting means that detects the conveying speed of the recording material in the fixing means, and the peripheral speed fluctuation is controlled by controlling the movement of the fixing means by the detecting means. Various image defects caused by the loop state of the recording material from the time when the recording material is nipped by the fixing means having a large size to the time when the recording material passes through the nip of the transfer means can be solved.

  Embodiments of the present invention will be described below.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a sectional view for explaining an outline of the configuration of an image forming apparatus according to an embodiment of the present invention. FIGS. 2 to 5 are partial detailed views from a secondary transfer unit to a fixing device and a paper discharge unit. 6 is a flowchart for explaining the operation.

  Since the flow of a series of image formation is known, it is omitted.

  The fixing device 100 that holds the film 101 as the fixing means and the pressure roller 104 is driven by a fixing motor M1 (not shown) that is the same drive source as the intermediate transfer belt 2.

  The fixing device 100 is mounted on the slide rail 44 so as to be movable along the conveyance direction of the recording paper P, and the rack 43 driven by the rotation of the gear 42 driven by the fixing device moving motor M2 (not shown) slides. Is moved by.

  Since the fixing device moving motor M2 only needs to move the position of the fixing device 100 at a speed higher than the speed at which the recording paper P is loosened (or pulled), a small, simple and inexpensive DC motor is used.

  At the center in the width direction of the conveyance guide 20 provided on the opposite side to the recording surface between the secondary transfer roller pair 3 and the fixing device 100 constituting the secondary transfer portion, the secondary transfer roller pair 3 and the fixing unit are fixed. A loop detection sensor arm 40 and a photo sensor 41 that constitute loop detection means for detecting a sag (loop) of the recording paper P caused by a difference in conveyance speed with the container 100 are arranged.

  When a predetermined loop amount is reached between the secondary transfer roller pair 3 and the fixing device 100, the loop detection sensor arm 40 blocks the light receiving portion of the photosensor 41, thereby detecting the loop.

  The transport guide 20 is divided into an upstream guide 20a and a downstream guide 20b. The upstream guide 20a is fixed to a holding member or the like of the secondary transfer roller 3 and does not move during recording, and the downstream guide 20b. Is fixed to the fixing device 100 and moves in conjunction with the movement of the fixing device 100.

  Even if the fixing device 100 moves and the position of the downstream guide 20b changes, the rear end of the upstream guide 20a and the front end of the downstream guide 20b are guided so that the front end of the recording paper P can be guided to the fixing device 100. It overlaps.

  The second conveyance guide 21 between the fixing device 100 and the paper discharge roller pair 8 has the same configuration.

  The conveyance speed of the recording material P in the discharge roller pair 8 is set to be the same as the conveyance speed of the recording paper P in the secondary transfer roller pair 3.

  In addition, a position detection sensor 45 for detecting the position (home position) of the fixing device 100 at the start of operation is provided, and a blocking flag 55 provided in the fixing device 100 blocks the light receiving unit, thereby fixing the fixing device 100. Detects the home position.

In this image recording apparatus, when the variation in the conveyance speed Vf of the recording paper P by the fixing device 100 with respect to the conveyance speed Vp of the recording paper in the secondary transfer roller pair 3 occurs up to X%, the fixing device 100 can be moved. The upstream side is Lfu, the downstream side is Lfl, the maximum recording paper length to be conveyed is Lp, and the distance between the secondary transfer roller pair 3 and the fixing device 100 before the start of movement (not the shortest distance but actually the recording paper) ) Is Ld (two-dot chain line in FIG. 2),
The time Td from when the leading edge of the recording paper P enters the fixing device 100 to when the trailing edge of the recording paper P passes through the secondary transfer portion 3 is:
Td = (Lp−Ld) / Vp Equation 1
And
If the maximum loop amount generated by the difference in transport speed between the secondary transfer unit 3 and the fixing device 100 is Lr,
Lr = (Vp−Vf) × Td Equation 2
When substituting equation 1 into equation 2,
Lr = (Vp−Vp × ((100 + X) / 100)) × (Lp−Ld) / Vp
= Vp × X / 100 × (Lp−Ld) / Vp
Lr = X / 100 × (Lp−Ld) Equation 3
It becomes.

  When X is negative, Lr becomes positive and the number of loops increases. When X is positive, Lr becomes negative, and the recording paper P is pulled between the secondary transfer unit 3 and the fixing device 100 by Lr due to the speed difference. Will be.

Assuming that the loop amount Lr1 increases from the loop amount of the paper in a state where the leading edge of the recording paper P enters the fixing device 100 until the loop detection sensor detects it, the movement amount Lfu of the fixing device 100 required on the upstream side is Lr. In the negative case, Lfu = | Lr | + Lr1 (4)
It becomes.

Further, the movement amount Lfl of the fixing device 100 required on the downstream side is when Lr is positive,
Lfl = Lr−Lr1 Formula 5
It becomes.

  The actual operation will be described below.

The speed Vp at the secondary transfer unit 3 is 120 mm / s, the speed Vf at the fixing device 100 is 120 mm / s ± 2% (± 2.4 mm / s), and the recording paper length Lp is 297 mm. And the distance Ld before the start of movement of the fixing device 100 is 50 mm, and the sag amount (loop amount) Lr1 of the recording paper P kept constant between the secondary transfer unit 3 and the fixing device 100 is 2 mm.
The amount of movement Lfu to the upstream side is expressed by Lfu = | Lr | −Lrl from Equation 3 and Equation 4.
= | X / 100 × (Lp−Ld) | −Lrl
= | -2 / 100 × (297-60) | -2
= 4.47 + 2
= 6.47 (mm)
The amount of movement Lfl to the downstream side is expressed by Lfl = Lr−Lr1 from Equation 3 and Equation 5.
= X / 100 * (Lp-Ld) -Lr1
= 2/100 x (297-60) -2
= 4.47-2
= 2.27 (mm)
It becomes.

  In this state, when the leading edge of the recording paper P enters the fixing device 100, the fixing device 100 is moved upstream. The moving speed may be set to a speed difference of 2.4 mm / s or more with respect to the secondary transfer unit 3 when the conveyance speed of the recording paper P in the fixing device 100 is the slowest.

  When the fixing device 100 is moved to the upstream side and the recording paper P is detected to have reached a predetermined loop by the bending loop detection sensor 41 and the state shown in FIG. 3 is reached, the fixing device 100 is moved to the downstream side to detect the loop. When 41 is turned off and the loop becomes smaller, the fixing device 100 is again moved upstream, and the loop detection sensor 41 detects the slack of the sheet. Thereafter, this is continued until the trailing edge of the recording paper P passes through the secondary transfer roller unit 3. Repeat the operation.

  When the paper conveyance speed in the fixing device 100 is faster than the conveyance speed of the secondary transfer unit 3, the fixing device 100 gradually moves upstream in order to prevent the recording paper P from being pulled after detecting the loop. I will do it.

  When the pressure roller 104 is sufficiently warmed or the like and the conveyance speed of the fixing device 100 is the fastest, the fixing device 100 finally moves 6.47 mm upstream from the operation start position. It becomes the state of.

  Further, when the sheet conveyance speed in the fixing device 100 is slower than the conveyance speed of the secondary transfer unit 3, the trace of detecting the loop is gradually moved downstream in order to prevent the loop from increasing. In the case where the recording paper transport speed is the slowest in the fixing device 100, it moves 2.27 mm downstream from the operation start position, resulting in the state shown in FIG.

  Before the trailing edge of the recording paper P comes out of the fixing device 5 and the next recording paper is conveyed, the fixing device starting motor M2 is driven, and the blocking flag 5b portion provided in the fixing device 5 detects the position. When the sensor 45 is shielded from light, the sensor 45 is stopped and positioned at the home position.

  Thereafter, the same operation is performed every time the recording paper is conveyed.

  The above operation will be described with reference to the flowchart of FIG.

  When a recording start signal is received, various operations necessary for image recording are started.

  When the transfer to the recording paper P is performed by the secondary transfer unit 3 and the leading edge of the recording paper P enters the fixing device 100, the loop detection sensor 41 is activated. If the sensor 41 is turned on and off again (after 50 msec in this embodiment) and is OFF, it is determined that the loop has not reached a predetermined amount, and the fixing device moving motor M2 is rotated in a predetermined direction. The fixing device 100 is moved upstream. Similarly, when the loop detection sensor 41 is ON, it is confirmed that the sensor 41 is turned ON / OFF again after a predetermined time. If the loop detection sensor 41 is ON, it is determined that the loop has exceeded a predetermined amount and the fixing device moving motor M2 is reversed And the fixing device 100 is moved downstream. If the detection of the sensor 41 is different after a predetermined time (50 msec), it is determined that the sensor 41 is chattering or the like, it is determined that the sensor 41 is not completely switched on or off, and the operation of moving the fixing device is not changed. The loop detection sensor 41 makes an ON / OFF determination again until the trailing edge of the recording paper P passes through the secondary transfer portion 3, and this operation is repeated thereafter, and the loop detection sensor 41 always repeats ON / OFF. Transport while maintaining a constant state.

  The fixing device moving motor M2 is stopped at the timing when the trailing edge of the recording paper P passes through the secondary transfer portion 3, and then the fixing device 100 is moved to the home position after the trailing edge of the recording paper P passes through the fixing device 100. .

  When recording on the recording paper P is continued, the process returns to the first various image recording operations. When recording is ended, various end sequences for stopping the operation are performed and the operation is ended.

  In this way, by moving the fixing device 100 and keeping the loop constant, the loop becomes too large even in a short conveyance path, and hits the conveyance guide, and the recording paper is pulled, thereby causing an image defect. As a result, it is possible to obtain a good image with no load and to drive the fixing device 100 having a large load torque and the intermediate transfer belt 2 with the same high torque motor.

  In addition, since the conveyance speed of the discharge roller is set to be equal to the conveyance speed of the secondary transfer unit between the fixing device and the discharge roller provided downstream of the fixing device and fixed to the apparatus, the fixing device As long as the recording paper maintains a constant loop amount between the secondary transfer unit and the secondary transfer unit, a constant loop amount is ensured between the fixing device and the paper discharge roller. Seat buckling and the like can be prevented.

  In this embodiment, a loop detection sensor is disposed in the conveyance path between the secondary transfer unit and the fixing device, and the movement of the fixing device is controlled by detecting the loop of the recording paper. When the position is required, use the fact that the driven film is the same as the transport speed of the recording paper. Mark the film and read the rotation speed with a sensor. It is also possible to control the movement of the fixing device in accordance with a loop amount between the fixing device and the fixing device.

  Further, in this embodiment, the moving amount of the fixing device is set differently on the upstream side and the downstream side, but the outer diameter of the pressure roller of the fixing device is changed according to the situation of the apparatus, and the secondary unit is changed. By changing the setting of the fixing device speed relative to the transfer portion conveyance speed, it is possible to make the movement amount the same or move to either one of them.

  A second embodiment of the present invention will be described with reference to FIGS.

  FIG. 7 is a cross-sectional view of the image forming apparatus adopting the present invention, and FIGS. 8 and 9 are perspective views of essential parts of the secondary transfer portion and the fixing device.

  The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In this embodiment, rails 64 and 74, gears 62 and 72 and racks 63 and 73 serving as fixing device moving means, and loop detection sensor arms serving as loop detecting means are provided at both ends in the width direction of the fixing device 100, respectively. 60 and 70 and photosensors 61 and 71 are provided.

  Further, the fixing device 100 is provided with blocking flags 55c and 55d and position sensors 65 and 75 for detecting the home positions at both ends, and the home position can be detected independently.

  In FIG. 7, only one can be seen because the cross-sectional arrangement is at the same position, but in actuality, as shown in the perspective view of FIG. 8, they are arranged at both ends in the width direction of the transport direction.

(In FIG. 8, gears 62 and 72, racks 63 and 73, photosensors 61 and 71, blocking flags 55c and 55d, and position sensors 65 and 75 are omitted.)
The rails 64 and 74 are not fixed to the fixing device 100, but are attached to the fixing device 100 so as to be rotatable about shafts 64a and 74a.

  In this embodiment, the gears 62 and 72 are independently driven by drive motors M3 and M4 (not shown) as moving means of the fixing device 100, as indicated by arrows A and B shown in FIG. Both end portions of the fixing device 100 can be moved independently.

  The actual operation is to control the fixing device moving motors M3 and M4 based on the signals of the respective loop detection sensors. The other operations and configurations are the same as in the first embodiment. Similar to the example.

  In such a configuration, the recording paper P is transferred and transported by the secondary transfer unit 3 and begins to be transported by the fixing device 100, and the driving motors M3 and M4 are driven to drive the fixing device 100 as in the first embodiment. Although the loop is kept constant by moving, the conveyance speed in the width direction of the recording paper P may be slightly different due to variations in the biasing pressure of the fixing device 100 and the secondary transfer unit 3 and tolerances. .

  When the length of the recording paper P is short, there is no problem because the difference in the size of the loop in the width direction is slight even in such a state, but a long paper or a large size recording paper P is conveyed. In this case, as shown in FIG. 9, one of the loops becomes too large and is rubbed against the conveyance guide 20, and on the opposite side, the recording paper P is pulled between the secondary transfer unit 3 and the fixing device 100. There is a case.

  Even in such a state, both sides of the fixing device 100 can be moved independently. Therefore, the side where the loop becomes larger (the front side in FIG. 9) before the state shown in FIG. If the side to be pulled and pulled (the back side in FIG. 9) is moved in the direction of arrow D, the loop can be made uniform.

  Since the above operation is performed in accordance with the output of the loop detection sensor, the image recording apparatus using this configuration does not actually enter the state shown in FIG. 9, but finally the fixing device 100 is tilted (in FIG. 9, The recording paper P is discharged from the fixing device 100 in a state where the front side is inclined upward and the back side is inclined downward.

  In the first and second embodiments, a dedicated motor is used to move the fixing device. However, driving is performed from the driving motor of the fixing device, and the driving is turned on and off by an electromagnetic clutch or the like, and the rotation direction is switched. You may go.

  In the first and second embodiments, the color electrophotographic image forming apparatus using the intermediate transfer belt is used. However, the present invention is not limited to this, and for example, a method of directly transferring from a photosensitive drum to a recording sheet. Black and white (single color) electrophotographic image recording apparatus, direct transfer type color electrophotographic image recording apparatus in which a plurality of photosensitive drums are arranged in parallel, and recording paper sequentially passes through the transfer section of each photosensitive drum. It is also possible to apply.

1 is a cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. It is principal part detailed sectional drawing in the 1st Example of this invention. It is principal part detailed sectional drawing in the 1st Example of this invention. It is principal part detailed sectional drawing in the 1st Example of this invention. It is principal part detailed sectional drawing in the 1st Example of this invention. It is principal part detailed sectional drawing in the 2nd Example of this invention. It is a principal part perspective view in the 2nd Example of this invention. It is a principal part perspective view in the 2nd Example of this invention. It is sectional drawing of the conventional image forming apparatus. It is sectional drawing of the fixing device of a film system It is a principal part sectional view of a conventional image forming apparatus. It is a principal part sectional view of a conventional image forming apparatus. It is a principal part sectional view of a conventional image forming apparatus.

Explanation of symbols

a to d Photosensitive drum
P Recording material
1a ~ 1d Process cartridge
2 Intermediate transfer belt
3 Secondary transfer roller pair
4 Paper cassette
5 Fixing unit
6 Exposure equipment
7 Discharge tray 20 First transport path 21 Second transport path 40, 60, 70 Loop detection lever 41, 61, 71 Detection sensor 42, 62, 72 Gear

Claims (4)

An image carrier that carries a latent image; a developing unit that visualizes the latent image on the latent image carrier as a developer image; a transfer unit that transfers the developer image to a recording material as an unfixed image; An image forming apparatus comprising: a fixing unit that fixes a received image to the recording material by heating; and a paper discharge conveying unit that discharges the recording material to the fixing unit.
A moving unit that allows the fixing unit to move in the conveyance direction of the recording material; and a loop detection unit that detects a slack state of the recording material between the transfer unit and the fixing unit.
An image forming apparatus characterized in that the movement of the fixing means is controlled by the loop detecting means for detecting the sag state.   The image forming apparatus according to claim 1, wherein the driving source of the fixing device and the transfer unit is the same driving source.   The moving means is provided at both ends of the fixing device in the width direction of the recording material, and loop detecting means is provided at portions corresponding to the both ends of the recording material, and the moving means is based on the detecting means corresponding to each side. The image forming apparatus according to claim 1, wherein the operation is performed. An image carrier that carries a latent image; a developing unit that visualizes the latent image on the latent image carrier as a developer image; a transfer unit that transfers the developer image to a recording material as an unfixed image; An image forming apparatus comprising: a fixing unit that fixes a received image to the recording material by heating; and a paper discharge conveying unit that discharges the recording material to the fixing unit.
A moving unit that enables the fixing unit to move in the conveyance direction of the recording material; and a detection unit that detects a conveyance speed of the recording material in the fixing unit.
An image forming apparatus, wherein the movement of the fixing unit is controlled by the detecting unit.

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